Phase-locked single-cycle transients with frequency components between 1 and 60 THz and peak fields of up to 12 MV=cm are generated as the idler wave of a parametric amplifier. To achieve broadband conversion in GaSe nonlinear crystals, we match the group velocities of signal and idler components. The influence of group-velocity dispersion is minimized by long-wavelength pumping at 1:18 μm. Free-space electro-optic sampling monitors the multiterahertz waveforms with direct field resolution.